A hydrocarbon resource such as petroleum or natural gas is recovered and produced from a well (an oil well or a gas well; may collectively be referred to as a “well”) including a porous and permeable subterranean formation. A downhole tool serving as a device configured to form a hole for forming such a well (in other words, a hole provided to form a well; may be referred to as a “downhole”) is used in high-temperature, high-pressure environments. Thus, each component constituting the downhole tool also need to have high strength. Furthermore, since the downhole tool is difficult to extract after use, a downhole tool component used in isolation and sealing applications needs to be degradable and removable in a location of use.
A component using a degradable resin or rubber has been used as the degradable and removable downhole tool component, but may have insufficient strength and heat resistance, and a metal or a non-degradable resin may be used for a component that needs to have high strength or high heat resistance. When the component including a metal or a non-degradable resin is used, the component needs to be broken into small fragments by milling or the like to be retrieved, and a cost and labor increase. Furthermore, a milling defect and a retrieval failure may cause production impediment. Furthermore, in the case of a downhole tool including a combination of a degradable resin or rubber and a non-degradable metal or resin, the non-degradable component remains in a well, and may cause production impediment. Thus, there is a demand for a metal component readily degradable after use.
Patent Documents 1 and 2 each describe use of a magnesium alloy material containing aluminum, lithium, calcium, yttrium, and the like in a product for subterranean work such as a petroleum well or a natural gas well, and each describe quick degradation of this magnesium alloy material.
Patent Document 3 describes a plug that is a downhole tool using a slip and a mandrel made of a magnesium alloy.
Patent Document 4 describes a magnesium alloy cast forged material having a reduced weight and being excellent in strength.